(a) Field of the Invention
The present invention relates to a flexible metal laminate, and more particularly, to a flexible metal laminate implementing a low dielectric constant, a high degree of elasticity, and an optimized thermal expansion coefficient, and also having a solid internal structure and high interlayer bonding strength.
(b) Description of the Related Art
A flexible metal laminated board is mainly used as a base material of a flexible printed circuit board, and additionally, is used in cotton heating elements, electromagnetic shield materials, flat cables, packaging materials, and the like.
Among the flexible metal laminated boards, there is a flexible copper foil laminated board that includes a polyimide layer and a copper foil layer, and it may be divided into a bonded type and a non-bonded type depending on whether there is an epoxy adhesive layer between the polyimide layer and the copper foil layer.
Herein, the non-bonded flexible copper foil laminated board is formed by directly bonding polyimide on a surface of copper foil, and according to recent trends of miniaturization and thickness reduction of electronic products, and of requiring an excellent ion migration property, the non-bonded type of flexible copper foil laminated board is mainly used.
Further, in accordance with trends of miniaturization and acceleration of electronic equipment, and combination of various functions, there has been a demand to improve a signal transmission speed to the inside or outside of electronic equipment.
Accordingly, development of a printed circuit board using an insulator having lower dielectric constant and dielectric loss factor than existing insulators is demanded.
Recently, reflecting these trends, an attempt has been made to use a liquid crystalline polymer (LCP) which is an insulator having a lower dielectric constant and a smaller effect on moisture absorption than a conventional polyimide in the flexible printed circuit board.
However, LCP does not have a better dielectric constant (Dk=2.9) than that of polyimide (Dk=3.2), has too low thermal resistance, and has poor compatibility with an existing PCB manufacturing process using polyimide. Therefore, a study on lowering the dielectric constant of the previously used polyimide has been conducted, rather than using LCP.
Meanwhile, although a flexible metal laminated board containing a fluorine resin represents a low dielectric constant and also has excellent applicability on a printed circuit board, the fluorine resin has been detected in an interface of a thermosetting polyimide layer in which the fluorine resin is dispersed, thereby lowering its adhesion to a thermoplastic polyimide layer.
Accordingly, a study on a flexible metal laminated board maintaining the dielectric constant and dielectric loss factor of the existing flexible metal laminated board containing the fluorine resin, and also having excellent interfacial adhesive strength, is currently required.